Coal-based porous carbon material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of supercapacitor materials, and particularly relates to a coal-based porous carbon material and a preparation method and application thereof. In order to solve the problems of safety, batch stability and easy formation of a pore structure in a process for preparing porous carbon from coal, the method comprises the following steps: firstly, carrying out mixing and kneading treatment on fine-particle raw material coal and a liquid-phase doping agent, and then carrying out drying-low-carbon integrated treatment on the mixture; then activating the low-carbon material at a high temperature by means of water vapor, and then performing refined pore-forming on the cavity structure at a high temperature by means of carbon dioxide gas; after the activation reaction is finished, carrying out impurity removal treatment on the activated material with the high specific surface area by virtue of an acid-base solution; and depositing a layer of organic polymer on the surface of the purified material by adopting an atomic layer deposition technology, and forming a passivation layer on the polymer layer by virtue of high-temperature treatment, thereby obtaining the coal-based porous carbon material with stable performance and structure, and further applying the coal-based porous carbon material to the negative pole piece of the supercapacitor.

Description

Technical Field

[0001] The present invention belongs to the technical field of supercapacitor materials, and particularly relates to a coal-based porous carbon material, a preparation method thereof, and an application thereof. Background Art

[0002] A supercapacitor is a new type of energy storage device between ordinary capacitors and batteries. With its advantages of high safety, fast charge and discharge speed, long cycle life, etc., it shows broad application prospects in the fields of electric vehicles, rail transit, new energy power generation, power frequency modulation, elevators, etc. In the entire new energy storage field, the industrialization development is relatively mature. In the future, with the market demands of military and civilian applications, etc., the industrial market application will develop by leaps and bounds. At present, after years of efforts in the domestic supercapacitor industry, China is the largest application market. Among them, porous carbon, as the core material of supercapacitors, is the key to the future development of high-performance and low-cost supercapacitors.

[0003] At present, the porous carbon used in supercapacitors mainly includes biomass-based, fossil-based (coal / pitch / petroleum coke / pitch coke, etc.) and polymer-based materials. Among them, coal has the advantages of rich reserves and low price as the raw material of porous activated carbon. However, at present, the preparation of porous negative electrode materials for supercapacitors from coal mostly adopts the method of alkali activation. In the preparation process, the alkali-carbon ratio ≥1 and the mixing method of alkali and materials is mostly an uneven mixing method, which results in great differences in the pore structures between batches of the prepared porous carbon materials, and the regulation of the internal pore structure of activated carbon is limited; on the other hand, during the high-temperature alkali activation process, alkali escapes and deposits in high-temperature equipment, and it is extremely easy to catch fire or explode when encountering air or water, resulting in serious safety problems. Therefore, researchers have developed a physical activation method to activate and regulate coal. However, for the ordered polycyclic aromatic hydrocarbon molecular structure in coal, the regulation degree of the structure of activated carbon by simple steam or carbon dioxide activation is limited. The main reason is that the polycyclic aromatic hydrocarbon molecular structure in coal is closely arranged. During the etching process with steam or carbon dioxide, it is difficult to penetrate into the aromatic hydrocarbon molecular structure. At the same time, the polycyclic aromatic hydrocarbon molecular structure is mostly a large lamellar structure, and the activation energy for the reaction of steam or carbon dioxide with carbon atoms in the polycyclic aromatic hydrocarbon molecular structure is relatively high.

[0004] Therefore, there is an urgent need to provide a preparation method of a coal-based porous carbon material to solve the problems of process safety, batch stability, and easy formation of pore structure in the preparation of porous carbon from coal. Summary of the Invention

[0005] The present invention provides a coal-based porous carbon material, a preparation method thereof, and an application thereof. In view of the above problems, the present invention modifies coal-based active sites with dopants and effectively exfoliates defect sites by means of physical combined activation, thereby forming a large number of microporous structures, solving the problem of difficult pore formation in coal activation. At the same time, this process avoids the safety problems caused by the escape and deposition of traditional high-temperature alkali treatment, and has the advantages of simple process and low cost.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides a preparation method of a coal-based porous carbon material, comprising the following steps:

[0008] (1) Crushing the raw coal to obtain a fine-particle-size crushed material, dissolving a water-soluble dopant in deionized water to obtain a liquid-phase dopant, and then kneading the fine-particle-size crushed material with the liquid-phase dopant to obtain a mixed material;

[0009] (2) Performing drying-low-carbon integration treatment on the mixed material to obtain a low-carbon material; performing combined activation treatment on the low-carbon material by stagewise introducing steam and carbon dioxide gas to obtain an activated material with a high specific surface area; purifying the activated material in a purification liquid to obtain a purified material;

[0010] (3) Subsequently, passivating the surface of the purified material by means of atomic layer deposition technology to obtain a passivated material, and then performing high-temperature carbonization treatment on the passivated material to obtain the coal-based porous carbon material.

[0011] The present invention first kneads fine-grained raw coal with a liquid-phase dopant. In this process, the liquid-phase dopant can be in full and uniform contact with the fine-grained raw material. Then, the mixed material is subjected to integrated drying and low-carbon treatment. Under high-temperature conditions, the dopant penetrates into the interior of the fine particles and undergoes a grafting reaction with the carbon atoms in the polycyclic aromatic hydrocarbons in the coal. After that, the low-carbon material is activated by steam at high temperature. During the steam activation process, it is easier to activate the position points doped with carbon, and pore structures are easily formed at these positions. Subsequently, the pore structure is refined by carbon dioxide gas at high temperature to form nm pore channels required for the negative electrode material of the supercapacitor. After the activation reaction is completed, the activated material with a high specific surface area is purified by an acid-base solution to remove ash and trace metal element contents. The surface of the activated and purified material contains a large number of dangling bonds or functional groups, and it is not suitable to be directly used as the negative electrode material of the supercapacitor. The atomic layer deposition technology is used to deposit an organic polymer on the surface of the purified material, and the polymer layer is formed into a passivation layer by high-temperature treatment, thereby obtaining a coal-based porous carbon negative electrode material with stable performance and structure. This process not only solves the problem of the difficulty in activating the coal structure by single steam or carbon dioxide, making the coal-based porous carbon have a rich nm pore structure and high electrochemical properties in supercapacitors, but also is safe, reliable, simple and feasible during the industrial scale-up process of this process, and can avoid cumbersome process flows.

[0012] Further, in the step (1), the particle size D50 of the fine-particle crushed material is 3-10 μm, and the mass ratio of the water-soluble dopant to deionized water is 3-15:100; the mass ratio of the fine-particle crushed material to the liquid-phase dopant is 12-20:100;

[0013] The raw coal is any one or at least two of anthracite, lean coal, meager coal, coking coal, fat coal, gas coal, weakly caking coal, non-caking coal, long-flame coal, and lignite;

[0014] The water-soluble dopant is at least one of a phosphorus-containing compound, a nitrogen-containing compound, an oxygen-containing compound, a boron-containing compound, and a fluorine-containing compound;

[0015] The phosphorus-containing compound is any one or at least two of diphosphorus trioxide, phosphorus pentoxide, phosphoric acid, sodium dihydrogen phosphate, diammonium hydrogen phosphate, phosphorus trichloride, ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate;

[0016] The nitrogen-containing compound is any one or at least two of ammonium carbonate, ammonium bicarbonate, ammonium sulfide, nitric acid, ammonium chloride, and ammonium sulfate;

[0017] The oxygen-containing compound is any one or two of sulfuric acid and hydrogen peroxide;

[0018] The boron-containing compound is any one or at least two of boron trifluoride, boric acid, boron trioxide, and calcium borate;

[0019] The fluorine-containing compound is any one or a combination of at least two of hydrogen fluoride and sodium fluoride.

[0020] Furthermore, in the step (1), the kneading treatment is carried out by a kneader, the kneading rotation speed is 25-35 r / min, and the kneading time is 1-3 h.

[0021] During the long-time kneading process of the soluble dopant and the solid-phase fine-particle coal in the step (1), uniform contact between the kneaded material and the dopant can be achieved.

[0022] Furthermore, in the step (2), the drying-low-carbon integrated treatment is carried out by a double-layer rotary furnace. The upper rotary furnace of the double-layer rotary furnace has no temperature setting, the rotation speed is 0.2-1.0 r / min, the heating rate is 2-5 °C / min, and the gas flow direction is reverse to the feeding direction. The gas flow temperature is mainly preheated and dried by the hot gas flow carried by the lower rotary furnace;

[0023] The final temperature of the lower rotary furnace of the double-layer rotary furnace is set at 450-750 °C, the rotation speed is 0.2-1.0 r / min, the heating rate is 2-5 °C / min, and the gas flow direction is reverse to the feeding direction.

[0024] In the step (2), the design and use of the double-layer rotary furnace effectively save the process cost of drying. By means of preheating and the direction of the reverse gas flow, the moisture of the wet material is removed.

[0025] Furthermore, in the step (2), the combined activation treatment is as follows: first, steam pore-forming activation is carried out, and then carbon dioxide fine pore structure regulation activation is carried out;

[0026] The activation temperature of the steam is 800-1000 °C, and the activation time is 2-5 h;

[0027] The ratio of the steam flow rate to the low-carbon material is 2-100 L / min: 1 kg;

[0028] The activation temperature of the carbon dioxide is 900-1000 °C, and the activation time is 2-10 h;

[0029] The ratio of the carbon dioxide flow rate to the low-carbon material is 10-50 L / min: 1 kg.

[0030] In the step (2), by means of the combined staged activation of steam and carbon dioxide, on the one hand, the polycyclic aromatic hydrocarbon doping sites in the coal are quickly activated by steam to form a pore structure; on the other hand, the formed pore structure is finely regulated by carbon dioxide gas to form the nm pore structure required for the negative electrode material of the supercapacitor.

[0031] Further, in the step (2), the purification liquid is a composite acid / alkali solution, and the purification treatment is as follows: the activated material is successively placed in the composite acid / alkali solution, and the metal impurities and other inorganic impurities are removed by using the characteristics of the acid / alkali solution;

[0032] The temperature of the purification treatment is 60-100°C, the time is 5-10h, and the stirring speed is 500-1000r / min;

[0033] The mass ratio of the high specific surface area activated material to the purification liquid is 1:2-10;

[0034] The acid solution is at least one of hydrochloric acid, hydrofluoric acid and oxidizing acid, and the concentration is 0.5-5mol / L;

[0035] The alkali solution is any one or at least two of sodium hydroxide, potassium hydroxide, barium hydroxide, ammonium hydroxide or calcium hydroxide, and the concentration is 0.5-5mol / L.

[0036] The appropriate treatment temperature in the step (2) is beneficial to promoting the acid / alkalization reaction for purification, and effectively removing the ash and impurities in the coal.

[0037] Further, in the step (3), the passivation treatment is as follows: under the condition of an inert atmosphere with a flow rate of 100-1000mL / min and an atomic layer deposition temperature of 100-300°C, organic polymer deposition is carried out for 2-10h to obtain a passivated material;

[0038] The organic polymer is one or two of polyamide, polyimide and polyacrylonitrile;

[0039] The inert gas is nitrogen, argon or a mixed gas of nitrogen and argon.

[0040] The appropriate deposition time in the step (3) can ensure the thickness of the deposition layer on the surface of the porous carbon, which is beneficial to the repair of the dangling bonds or defects on the surface of the porous carbon.

[0041] Further, in the step (3), the high-temperature carbonization treatment is as follows: in an inert atmosphere, first program the temperature and then cool naturally;

[0042] The temperature programming is to increase the temperature to 850-1050°C at a heating rate of 2-10°C / min;

[0043] The time of the high-temperature carbonization treatment is 1-10h.

[0044] The appropriate carbonization temperature in the step (3) is beneficial to the passivation of the surface organic polymer layer and the secondary shrinkage of some pores inside the porous carbon.

[0045] The present invention also provides a coal-based porous carbon material prepared by the above preparation method. This material is a porous material with a rich microporous channel structure, high structural strength and a relatively stable surface layer structure.

[0046] The present invention also provides an application of the coal-based porous carbon material in a supercapacitor.

[0047] Compared with the prior art, the present invention has the following advantages:

[0048] First, the present invention kneads fine particle raw coal with a liquid-phase dopant. In this process, the liquid-phase dopant can be in full and uniform contact with the fine particle raw material. Then, the mixed material is subjected to drying-low-carbon integration treatment, and the dopant penetrates into the interior of the fine particles and undergoes a grafting reaction with the carbon atoms in the polycyclic aromatic hydrocarbons in the coal under high-temperature conditions. After that, the low-carbon material is activated by steam at high temperature. In the steam activation process, it is easier to activate the carbon-doped position points, and void structures are easily formed there. Subsequently, the void structures are finely pore-formed by carbon dioxide gas at high temperature to form nm pores required for the negative electrode material of the supercapacitor. After the activation reaction is completed, the high-specific-surface activated material is purified by an acid-base solution to remove ash and trace metal element contents. The surface of the activated-purified material contains a large number of dangling bonds or functional groups, and it is not suitable to be directly used as the negative electrode material of the supercapacitor. An organic polymer is deposited on the purified material surface by atomic layer deposition technology, and a passivation layer is formed by means of high-temperature treatment, thereby obtaining a coal-based porous carbon negative electrode material with stable performance and structure. This process not only solves the problem of the difficulty in activating the coal structure by single steam or carbon dioxide, making the coal-based porous carbon have a rich nm pore structure and high electrochemical properties in supercapacitors, but also is safe, reliable, simple and easy to implement in the industrial scale-up process of this process, and can avoid cumbersome process flows. Description of the Drawings

[0049] Figure 1 It is the process flow chart provided by Example 1 in the present invention.

[0050] Figure 2 It is the SEM diagram of the coal-based porous carbon material provided by Example 1 in the present invention.

[0051] Figure 3 It is the micropore size distribution diagram of the coal-based porous carbon provided by Example 1 in the present invention. Detailed Embodiments

[0052] In order to further elaborate the technical solution of the present invention, the present invention is further described below through examples.

[0053] Example 1

[0054] As shown in Figure 1 the figure, a preparation method of a coal-based porous carbon material according to this embodiment includes the following steps:

[0055] (1) Crush the raw coal (long-flame coal) to a particle size D50 of 5 μm to obtain a fine-particle-size crushed material. Dissolve the water-soluble dopant (diammonium hydrogen phosphate) and water according to a mass ratio of 15:100 to obtain a liquid-phase dopant. Then, mix the obtained fine-particle-size crushed material and the liquid-phase dopant according to a mass ratio of 100:12, and use a kneader to perform kneading treatment for 2 h under the kneading condition of a rotation speed of 35 r / min to obtain a mixed material;

[0056] (2) Perform drying-low-carbon integration treatment on the obtained mixed material in a double-layer rotary furnace. The upper rotary furnace is not set with a temperature, the rotation speed is 0.2 r / min, the heating rate is 2 °C / min, and the gas flow direction is reverse to the feeding direction. The final temperature of the lower rotary furnace is set to 650 °C, the rotation speed is 0.5 r / min, the heating rate is 2 °C / min, and the gas flow direction is reverse to the feeding direction. After the reaction, a low-carbon material is obtained;

[0057] Perform combined activation treatment on the low-carbon material by periodically introducing steam and carbon dioxide gas, that is, first introduce steam according to the ratio of steam flow rate to low-carbon material of 10 L / min:1 kg to perform pore-forming activation treatment on the low-carbon material for 2 h at a temperature of 900 °C. Then, introduce carbon dioxide gas according to the ratio of carbon dioxide to low-carbon material of 10 L / min:1 kg to perform pore structure modification activation on the steam-activated material for 5 h at a temperature of 900 °C to obtain an activated material with a high specific surface area;

[0058] Perform purification treatment on the activated material in a purification solution, that is, place the activated material in a composite acid / alkali solution successively, and use the characteristics of the acid / alkali solution to remove metal impurities and other inorganic impurities. Perform purification treatment for 10 h under the conditions of 80 °C, a mass ratio of the activated material to the composite acid / alkali solution of 1:3, and a rotation speed of 1000 r / min to obtain a purified material;

[0059] Among them, the acid solution is hydrochloric acid with a concentration of 1 mol / L; the alkali solution is sodium hydroxide with a concentration of 1 mol / L.

[0060] (3) Deposit an organic polymer (polyamide) for 5 h at a flow rate of 200 mL / min of an inert atmosphere (nitrogen) and an atomic layer deposition temperature of 300 °C to obtain a passivated material; perform high-temperature carbonization treatment for 2 h in an inert atmosphere (nitrogen). The temperature of the high-temperature carbonization treatment is 1050 °C and the heating rate is 2 °C / min. After natural cooling, the coal-based porous carbon material is obtained.

[0061] Figure 2It is an electron microscope photograph of coal-based porous carbon. It can be seen from the figure that the coal-based porous carbon has an irregular shape and a relatively smooth surface; Figure 3 It is the gas adsorption and desorption curve of coal-based porous carbon. It can be seen that the prepared coal-based porous carbon is mainly composed of micropores, and the pore size is concentrated below 1 nm.

[0062] Example 2

[0063] (1) The raw coal (anthracite) was crushed to a particle size D50 of 10 μm to obtain a fine particle size crushed material. The water-soluble dopant (ammonium carbonate) and water were dissolved according to a mass ratio of 10:100 to obtain a liquid-phase dopant. The obtained fine particle size crushed material and the liquid-phase dopant were mixed at a mass ratio of 100:20, and a kneading machine was used to perform a kneading treatment for 1 h under the kneading condition of a rotation speed of 25 r / min to obtain a mixed material;

[0064] (2) The obtained mixed material was subjected to drying-low carbon integration treatment in a double-layer rotary furnace. The upper rotary furnace was not set with a temperature, the rotation speed was 0.5 r / min, the heating rate was 5 °C / min, the gas flow direction was reverse to the feeding direction, the final temperature of the lower rotary furnace was set at 750 °C, the rotation speed was 1.0 r / min, the heating rate was 5 °C / min, the gas flow direction was reverse to the feeding direction, and after the reaction, a low-carbon material was obtained;

[0065] The low-carbon material was subjected to combined activation treatment by periodically introducing steam and carbon dioxide gas. That is, first, steam was introduced according to the ratio of steam flow rate to low-carbon material of 5 L / min:1 kg to perform pore-forming activation treatment on the low-carbon material for 5 h at a temperature of 800 °C. Then, carbon dioxide gas was introduced according to the ratio of carbon dioxide to low-carbon material of 50 L / min:1 kg to perform pore structure modification activation on the steam-activated material for 2 h at a temperature of 1000 °C to obtain an activated material with a high specific surface area;

[0066] The activated material was purified in a purification solution, that is, the activated material was successively placed in a composite acid / alkali solution, and the acid / alkali solution characteristics were used to remove metal impurities and other inorganic impurities. Purification treatment was carried out for 8 h under the conditions of 100 °C, a mass ratio of activated material to composite acid / alkali solution of 1:10, and a rotation speed of 500 r / min to obtain a purified material.

[0067] Among them, the acid solution is hydrofluoric acid with a concentration of 2 mol / L, and the alkali solution is potassium hydroxide with a concentration of 5 mol / L.

[0068] (3) Deposit the organic polymer (polyimide) for 10 h at a flow rate of 100 mL / min in an inert atmosphere (argon) and an atomic layer deposition temperature of 100 °C to obtain a passivation material; conduct a high-temperature carbonization treatment for 10 h in an inert atmosphere (argon), where the temperature of the high-temperature carbonization treatment is 850 °C and the heating rate is 5 °C / min, and the coal-based porous carbon material is obtained after natural cooling.

[0069] Example 3

[0070] (1) Crush the raw coal (lignite) to a particle size D50 of 10 μm to obtain a crushed material, dissolve the water-soluble dopant (phosphorus pentoxide) and water in a mass ratio of 15:100 to obtain a liquid-phase dopant, and mix the obtained crushed material and the liquid-phase dopant in a mass ratio of 100:18, using a kneader, and conduct a kneading treatment for 3 h under the kneading condition of a rotation speed of 30 r / min to obtain a mixed material;

[0071] (2) Conduct a drying-low-carbon integration treatment on the obtained mixed material in a double-layer rotary furnace. The upper rotary furnace is not set with a temperature, the rotation speed is 1.0 r / min, the heating rate is 5 °C / min, the gas flow direction is reverse to the feeding direction, the final temperature of the lower rotary furnace is set at 550 °C, the rotation speed is 0.2 r / min, the heating rate is 2 °C / min, the gas flow direction is reverse to the feeding direction, and a low-carbon material is obtained after the reaction ends;

[0072] Stagewise introduce steam and carbon dioxide gas to conduct a combined activation treatment on the low-carbon material, that is, first introduce steam according to the ratio of the steam flow rate to the low-carbon material of 100 L / min:1 kg to conduct a pore-forming activation treatment on the low-carbon material for 2 h at a temperature of 1000 °C, and then introduce carbon dioxide gas according to the ratio of carbon dioxide to the low-carbon material of 10 L / min:1 kg to conduct a pore structure modification activation on the steam-activated material for 5 h at a temperature of 950 °C to obtain an activated material with a high specific surface area;

[0073] Conduct a purification treatment on the activated material in a purification liquid, that is, place the activated material in a composite acid / alkali solution successively, and use the characteristics of the acid / alkali solution to remove metal impurities and other inorganic impurities, and conduct a purification treatment for 6 h at 60 °C, with the mass ratio of the activated material to the composite acid / alkali solution being 1:5 and a rotation speed of 800 r / min to obtain a purified material.

[0074] Among them, the acid solution is sulfuric acid with a concentration of 5 mol / L, and the alkali solution is barium hydroxide with a concentration of 5 mol / L.

[0075] (3) Deposit the organic polymer (polyacrylonitrile) for 6 h at a flow rate of 500 mL / min in an inert atmosphere (nitrogen) and an atomic layer deposition temperature of 200 °C to obtain a passivation material; perform high-temperature carbonization treatment for 8 h in an inert atmosphere (nitrogen), the temperature of the high-temperature carbonization treatment is 900 °C, and the heating rate is 10 °C / min. After natural cooling, the coal-based porous carbon material is obtained.

[0076] Example 4

[0077] The difference between this example and Example 1 is that the kneading time in step (1) is less than 1 h.

[0078] The remaining preparation methods and parameters are the same as those in Example 1.

[0079] Example 5

[0080] The difference between this example and Example 1 is that the kneading time in step (1) is greater than 3 h.

[0081] The remaining preparation methods and parameters are the same as those in Example 1.

[0082] In the present invention, during the long-term kneading process of the soluble dopant and the solid-phase fine particle coal, uniform contact between the kneaded material and the dopant can be achieved.

[0083] Example 6

[0084] The difference between this example and Example 1 is that in step (2), a single rotary kiln is used for integrated drying and low-carbon treatment.

[0085] The remaining preparation methods and parameters are the same as those in Example 1.

[0086] Example 7

[0087] The difference between this example and Example 1 is that in step (2), the double-layer rotary kiln adopts a forward air flow, that is, the gas flow direction is forward with the feed.

[0088] The remaining preparation methods and parameters are the same as those in Example 1.

[0089] In the present invention, the design and use of the double-layer rotary kiln effectively save the process cost of drying, and realize the moisture removal of wet materials by means of preheating and the direction of reverse air flow.

[0090] Example 8

[0091] The difference between this example and Example 1 is that in step (2), single steam activation is used and carbon dioxide activation is not used.

[0092] The remaining preparation methods and parameters are the same as those in Example 1.

[0093] Example 9

[0094] The difference between this example and Example 1 is that in step (2), single carbon dioxide activation is used instead of steam activation.

[0095] The remaining preparation methods and parameters are the same as those in Example 1.

[0096] In the present invention, by means of the combined staged activation of steam and carbon dioxide, on the one hand, the polycyclic aromatic hydrocarbon doping sites in coal are quickly activated by steam to form a pore structure; on the other hand, the formed pore structure is finely regulated by carbon dioxide gas to form the nm pore structure required for the negative electrode material of the supercapacitor.

[0097] Example 10

[0098] The difference between this example and Example 1 is that in step (3), the atomic layer deposition time is less than 2 h.

[0099] The remaining preparation methods and parameters are the same as those in Example 1.

[0100] Example 11

[0101] The difference between this example and Example 1 is that in step (3), the atomic layer deposition time is greater than 10 h.

[0102] The remaining preparation methods and parameters are the same as those in Example 1.

[0103] In the present invention, an appropriate deposition time can ensure the thickness of the deposition layer on the surface of the porous carbon, which is beneficial to the repair of the dangling bonds or defects on the surface of the porous carbon.

[0104] Example 12

[0105] The difference between this example and Example 1 is that in step (3), the carbonization temperature is less than 850 °C.

[0106] The remaining preparation methods and parameters are the same as those in Example 1.

[0107] Example 13

[0108] The difference between this example and Example 1 is that in step (3), the carbonization temperature is greater than 1050 °C.

[0109] The remaining preparation methods and parameters are the same as those in Example 1.

[0110] In the present invention, an appropriate carbonization temperature is beneficial to the passivation of the surface organic polymer layer and the secondary shrinkage of some pores inside the porous carbon.

[0111] Comparative Example 1

[0112] The difference between this comparative example and Example 1 is that in step (1), no water-soluble liquid dopant is used.

[0113] The remaining preparation methods and parameters are the same as those in Example 1.

[0114] Performance Test

[0115] I. Physicochemical property test of coal-based porous carbon: (1) Specific surface area test: Test its specific surface area according to the national standard GB / T - 24533 - 2019 "Graphite Anode Materials for Lithium-ion Batteries"; (2) Pore size test: Test the pore size of the porous carbon obtained in the examples and comparative examples according to the national standard GB / T - 38949 - 2020 "Standard Particle Method for Determination of Pore Size of Porous Membranes".

[0116] II. Electrochemical performance test of coal-based porous carbon supercapacitor:

[0117] Use the coal-based porous carbon materials provided in the above examples and comparative examples as the supercapacitor electrode sheets, and then assemble them with a separator and electrolyte to obtain a button-type supercapacitor. The specific steps include:

[0118] Mix the coal-based porous carbon material, conductive carbon black, sodium carboxymethyl cellulose, SBR and solvent water in a certain proportion to obtain an electrode slurry, and then coat it on an aluminum foil. After drying, an electrode sheet is obtained; stack the electrode sheet and the separator (i.e., cellulose) in sequence to make a battery core; inject the electrolyte (quaternary ammonium salt, solvent is PC) into the core, and then seal it to obtain a button-type supercapacitor.

[0119] Perform specific capacitance and 5000-cycle capacity retention rate tests on the above button-type supercapacitor.

[0120] The test conditions are: charge / discharge at 0.5 A / g, the window voltage is set to 0 - 2.7 V, and the specific capacitance and cycle capacity retention rate of the battery are tested.

[0121] The test results are shown in Table 1.

[0122] Table 1 Test Results

[0123]

[0124] As can be seen from the above table, the preparation method provided by the present invention solves the problems of difficult alkali treatment and reaction uniformity during the chemical activation process. At the same time, the prepared porous carbon has a high specific surface area and a small pore structure, high electrochemical properties and good cycling properties.

[0125] As can be seen from Example 1 and Examples 4-5, if the kneading time is too short, the raw coal and the dopant cannot be well mixed together, resulting in larger pore diameters and smaller specific surface areas during the activation process; if the kneading time is too long, there is severe heat generation due to the friction between the material and the side wall during long-term kneading, and there are potential spontaneous combustion safety problems.

[0126] As can be seen from Example 1 and Examples 6-7, if only a single rotary kiln or a double-layer rotary kiln (with the gas flow in the same direction) is used, the kneaded material cannot be completely dried, resulting in a high moisture content, which affects the combination of polycyclic aromatic hydrocarbons and the dopant in the low-carbon material and the activation effect of the porous carbon.

[0127] As can be seen from Example 1 and Examples 8-9, if only steam activation or carbon dioxide activation is used, the effect of pore channel regulation is poor, and it is difficult to make the average pore diameter of the pore channels less than 2 nm.

[0128] As can be seen from Example 1 and Examples 10-11, if the atomic layer deposition thickness is relatively thin, the defect repair effect on the surface of the porous carbon is poor, and the cycling properties of the supercapacitor are poor; if the atomic deposition thickness is relatively large, it will cause an increase in process energy consumption.

[0129] As can be seen from Example 1 and Examples 12-13, if the carbonization temperature is relatively low, the influence on the surface passivation and the internal pore channel structure of the porous carbon is relatively small; if the carbonization temperature is relatively high, it will cause the collapse of the internal pore channels and a decrease in the specific surface area.

[0130] As can be seen from Example 1 and Comparative Example 1, if no dopant is used in step (1), the specific surface area generated during the subsequent steam activation process is relatively small, which is not conducive to the electrochemical properties of the supercapacitor.

[0131] The above shows and describes the main features and advantages of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to include all changes falling within the meaning and scope of the equivalent elements of the claims in the present invention.

[0132] In addition, it should be understood that although this specification is described according to the embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a coal-based porous carbon material, characterized in that: The following steps are involved: (1) crushing the raw coal to obtain a fine-particle crushed material, dissolving a water-soluble dopant in deionized water to obtain a liquid-phase dopant, and kneading the fine-particle crushed material and the liquid-phase dopant to obtain a mixed material; (2) subjecting the mixed material to an integrated drying-low carbon treatment to obtain a low carbon material; introducing water vapor and carbon dioxide gas in stages to perform a combined activation treatment on the low carbon material to obtain an activated material with a high specific surface area; and purifying the activated material in a purification solution to obtain a purified material; (3) The surface of the purified material is then passivated by means of atomic layer deposition technology to obtain a passivated material, and the passivated material is then subjected to high-temperature carbonization to obtain the coal-based porous carbon material.

2. The method for preparing a coal-based porous carbon material according to claim 1, characterized in that: In the step (1), the particle size D50 of the fine-particle crushed material is 3 to 10 μm, the mass ratio of the water-soluble dopant to deionized water is 3 to 15:100; the mass ratio of the fine-particle crushed material to the liquid phase dopant is 12 to 20:100; The raw coal is any one or at least two of anthracite, lean coal, lean coal, coking coal, fat coal, gas coal, weakly sticky coal, non-sticky coal, long flame coal and lignite; The water-soluble dopant is at least one of a phosphorus-containing compound, a nitrogen-containing compound, an oxygen-containing compound, a boron-containing compound, and a fluorine-containing compound; The phosphorus-containing compound is any one or at least two of phosphorus trioxide, phosphorus pentoxide, phosphoric acid, sodium dihydrogen phosphate, diammonium hydrogen phosphate, phosphorus trichloride, ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate; The nitrogen-containing compound is any one or at least two of ammonium carbonate, ammonium bicarbonate, ammonium sulfide, nitric acid, ammonium chloride, and ammonium sulfate; The oxygen-containing compound is any one or two of sulfuric acid and hydrogen peroxide; The boron-containing compound is any one or at least two of boron trifluoride, boric acid, boron trioxide, and calcium borate; The fluorine-containing compound is any one of hydrogen fluoride and sodium fluoride, or a combination of at least two of them.

3. The method for preparing a coal-based porous carbon material according to claim 1, characterized in that: The kneading treatment in step (1) is carried out by a kneading machine, the kneading speed is 25 to 35 r / min, and the kneading time is 1 to 3 hours.

4. The method for preparing a coal-based porous carbon material according to claim 1, characterized in that: In step (2), the drying-low carbon integrated treatment adopts a double-layer rotary kiln, the upper rotary kiln of the double-layer rotary kiln is not set to a temperature, the rotation speed is 0.2-1.0 r / min, the heating rate is 2-5°C / min, the gas flow direction is opposite to the feed, and the air flow temperature is preheated and dried by the hot air flow carried by the lower rotary kiln; The final temperature of the lower rotary kiln of the double-layer rotary kiln is set to 450-750° C., the rotation speed is 0.2-1.0 r / min, the heating rate is 2-5° C. / min, and the gas flow direction is reverse to the feed direction.

5. The method for preparing a coal-based porous carbon material according to claim 1, characterized in that: The combined activation treatment in step (2) is: firstly performing water vapor pore-forming activation and then performing carbon dioxide fine pore structure regulation activation; The activation temperature of the water vapor is 800-1000°C, and the activation time is 2-5h; The ratio of the water vapor flow rate to the low carbon material is 2-100 L / min:1 kg; The activation temperature of the carbon dioxide is 900-1000°C, and the activation time is 2-10h; The ratio of the carbon dioxide flow rate to the low carbon material is 10-50 L / min:1 kg.

6. The method for preparing a coal-based porous carbon material according to claim 1, characterized in that: In step (2), the purified liquid is a composite acid / base solution, and the purification process is as follows: placing the activated material in the composite acid / base solution in turn, and utilizing the characteristics of the acid / base solution to remove metal impurities and other inorganic impurities; The purification treatment is carried out at a temperature of 60 to 100°C, for a time of 5 to 10 hours, and at a stirring speed of 500 to 1000 r / min; The mass ratio of the activated material to the purified liquid is 1:2-10; The acid solution is at least one of hydrochloric acid, hydrofluoric acid and oxidizing acid, and the concentration is 0.5-5 mol / L; The alkaline solution is any one or at least two of sodium hydroxide, potassium hydroxide, barium hydroxide, ammonium hydroxide or calcium hydroxide, and the concentration is 0.5-5 mol / L.

7. The method for preparing a coal-based porous carbon material according to claim 1, characterized in that: The passivation treatment in step (3) is as follows: an organic polymer is deposited for 2 to 10 hours under the conditions of an inert atmosphere with a flow rate of 100 to 1000 mL / min and an atomic layer deposition temperature of 100 to 300° C. to obtain a passivation material; The organic polymer is one or two of polyamide, polyimide and polyacrylonitrile; The inert gas is one or both of nitrogen and argon.

8. The method for preparing a coal-based porous carbon material according to claim 1, characterized in that: The high temperature carbonization treatment in step (3) is: in an inert atmosphere, firstly programmed heating and then naturally cooling; The programmed temperature rise is to raise the temperature to 850-1050°C at a heating rate of 2-10°C / min; The high temperature carbonization treatment time is 1 to 10 hours.

9. A coal-based porous carbon material obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the coal-based porous carbon material according to claim 9 in a supercapacitor.

Images